Kelp Bass Essential Fishery Information

Kelp bass are an important recreationally fished species that is closely associated with kelp habitat. They form small, broadly distributed spawning aggregations. Like barred sand bass, kelp bass have ranked among the top ten sport fish caught by commercial passenger fishing vessels (CPFVs) in southern California. Both basses were managed under the same bag and size limits for over 50 years; however, fishery-dependent and fishery-independent data sources suggest significant population declines over the last decade and growing concerns regarding these fisheries have led to implementation of new size and bag limits.

Essential Fishery Information (EFI) includes data on age, growth, reproduction, and other life history characteristics that are important for managing a sustainable fishery. Data on several reproductive, age, and growth parameters for kelp bass are outdated or lack adequate sample sizes, and no data exist on kelp bass spawning periodicity (fluctuations in reproductive hormone levels). These EFI are needed to evaluate the fishery's response to recent and future regulation changes, as well as oceanographic changes. In addition, these EFI will be critical components of future stock assessments and Fishery Management Plans (FMPs), further enhancing CDFW's ability to manage this species.

Spawning Frequency

If a female has recently spawned, postovulatory follicles will be present in the ovaries. When we know what proportion of females have postovulatory follicles, we can estimate spawning frequency. In a previous study conducted 25 years ago over a brief portion of the spawning season, a small sample size indicated that female kelp bass spawn approximately every two and a half days. In 2013, we examined the current spawning frequency exhibited by kelp bass over the course of the entire spawning season.

Results coming soon!

Example of a histological section of a bass ovary showing a post ovulatory follicle (POF) surrounded by oocytes in various stages of development (Photo: CDFW).

Spawning Periodicity

Fish spawning is triggered by environmental cues. In marine environments, common cues include lunar and/or tidal flux. These cues are important for species to successfully reproduce and may indicate the best times for survival of fertilized eggs and larvae. Kelp bass may experience other environmental cues such as increased day length or increased temperature that drive them to form spawning aggregations, but there may be additional, closely related environmental cues throughout the spawning season that trigger spawning pulses. Understanding which cues trigger spawning in kelp bass is important for understanding how and why reproductive potential sometimes varies from year to year.

Reproductive hormones fluctuate with respect to environmental cues and may peak during spawning pulses. With support from the Reproductive Biology Lab run by Dr. Kelly Young at California State University Long Beach, we used enzyme immunoassays to measure the concentration of estradiol in the blood plasma collected from kelp bass over the course of the 2013 spawning season to estimate spawning periodicity.

We also looked at how hormone concentrations relate to fish size, gonad size and the presence or absence of post-ovulatory follicles produced by females following spawning events.

Results coming soon!

Batch Fecundity

Kelp bass are serial spawners, meaning they may spawn many times over the course of a spawning season. As in other serial spawners, kelp bass ovaries contain eggs at several different stages of development; however, only the hydrated eggs will be spawned.

Batch fecundity refers to the number of eggs released in one spawning event. By determining the batch fecundity for several individuals over a wide size range, we can develop a batch fecundity-size relationship which allows us to estimate the batch fecundity of females measured in the field. Batch fecundity will be an important parameter for estimating reproductive potential of kelp bass.

Staff counted the number of hydrated eggs in the ovaries to determine batch fecundity for individual fish.

Age Structure and Validation

The age of many fish can be determined by analysis of their otoliths. Otoliths are hard structures located in the inner ear that grow as the fish grows by adding layers of calcium carbonate. The addition of layers is affected by seasonal changes in growth rate, so that calcium carbonate rings may form annually and can be counted similar to tree rings. By counting the rings on the otoliths we can estimate the age structure of kelp bass. We are collecting otoliths from kelp bass in 2013.

While examining otoliths is a common ageing technique in fish, no one has ever validated that the ring pattern is annual across size classes in kelp bass. To examine this, we will keep kelp bass of several size classes in captivity for at least one year. Shortly upon capture we will inject a chemical marker called oxytetracyline (OTC) into the musculature that will be naturally incorporated into the otoliths. After a year, we will remove the otoliths and confirm the periodicity of the ring pattern.